Air supply system

ABSTRACT

An air supply system is provided that can reduce noise of a compressor and over a wider frequency band, along with the space and cost. The air supply system includes a compressor that draws in gas to discharge the drawn in gas at an increased pressure, an intake flow path  43  in which the gas drawn in by the compressor flows, a discharge flow path  44  in which the gas discharged from the compressor  41  flows, and rectification apparatuses  45 A and  45 B that are disposed in the vicinity of the compressor  41  in the intake flow path  43  and the discharge flow path  44 , respectively, and that rectify gas flowing therein.

This application is based on and claims the benefit of priority from Japanese Patent Application No. 2006-108339 Filed on Apr. 11, 2006, and Japanese Patent Application No. 2007-102458, filed on Apr. 10, 2007 the content of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an air supply system.

2. Related Art

Recently, fuel cell systems have attracted attentions as a new power source for automobiles. A fuel cell system includes, for example, a fuel cell for generating power by a chemical reaction of the reaction gas, a reaction gas supply apparatus for supplying reaction gas to the fuel cell via a reaction gas flow path, and a control apparatus for controlling the reaction gas supply apparatus.

A fuel cell has a stacked structure in which, for example, a few dozen or several hundred cells are layered. In this structure, each cell is composed of a pair of separators sandwiching a membrane electrode assembly (MEA). The membrane electrode assembly is composed of two electrodes, an anode (positive electrode) and a cathode (negative electrode), and a solid polymer electrolyte membrane sandwiched by these electrodes.

When hydrogen gas as a reaction gas is supplied to the anode of the fuel cell and air including oxygen as a reaction gas to the cathode, power is generated by way of an electrochemical reaction. This power generation basically produces only neutral water. Thus, fuel cells have attracted attention from the viewpoint of an influence on environmental impact and operational efficiency.

Incidentally, the above-described reaction gas supply apparatus includes, for example, a compressor which draws in air from the outside and discharges the drawn in air at high pressure.

This compressor includes a discharge outlet from which the compressed air at high pressure rapidly reduces pressure and causes turbulence. Such turbulence or pulsation of air causes a lot of noise.

In order to solve this problem, the discharge outlet of the compressor frequently includes a silencer (see Japanese Unexamined Patent Application Publication No. 8-69286).

In order to reduce noise, a structure has been suggested in which compressed air in the compressor can be gradually discharged by using a different shape of a discharge port of the compressor (see Japanese Unexamined Patent Application Publication No. 8-338387). Another structure has also been suggested in which the flow of air drawn into the compressor is mitigated by changing the shape of an intake port of the compressor.

SUMMARY OF THE INVENTION

When the above-described silencer is used to reduce noise, a larger sized case is needed to enclose the silencer. In this case, the installation space and weight of the silencer increases, and also causes an air pressure drop due to the silencer.

Furthermore, although changing the shape of the discharge port or the intake port can reduce noise in a specific narrow frequency band, reducing noise in a wide frequency band is difficult.

It is an objective of the present invention to provide an air supply system of smaller size and lower cost which can reduce compressor noise in a wider frequency band.

In a first aspect of the present invention, an air supply system (e.g., air supply system 21 in an embodiment), including a compressor which draws in gas to discharge the gas drawn in at an increased pressure (e.g., compressor 41 in an embodiment), an intake flow path in which the gas drawn in by the compressor flows (e.g., intake flow path 43 in an embodiment), a discharge flow path through which the gas discharged from the compressor flows (e.g., discharge flow path 44 in an embodiment), and a first rectification apparatus (e.g., rectification apparatus 45A in an embodiment), disposed in the vicinity of the compressor in the discharge flow path of the compressor and which rectifies gas flowing therein

The gas may be, for example, air containing oxygen.

According to the present invention, the discharge flow path includes the rectification apparatus for rectifying gas. Thus, even when a turbulence associated with a shock wave is caused by gas discharge, this turbulence can be rectified and a rapid change in the gas flow can be suppressed, thereby reducing the noise during gas discharge over a wide frequency band.

Consequently, as a result of the rectification apparatus being only provided at the discharge outlet of the compressor, the noise of the compressor can be reduced, along with a reduction in space and with a lower cost.

According to the present invention, even when gas is discharged causing turbulence associated with a shock wave, the turbulence can be rectified and a rapid change in the gas flow can be suppressed to reduce noise in a wide frequency band when gas is discharged. Thus, the present invention only requires a rectification apparatus to be provided at a discharge outlet of a compressor. Thus, the noise of the compressor can be reduced, along with reduced space and cost.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a block diagram of a fuel cell system using an air supply system;

FIG. 2 illustrates a block diagram of the schematic structure of the air supply system;

FIG. 3 illustrates a partial enlarged view of an intake flow path and a discharge flow path of the air supply system;

FIG. 4 shows the first illustrative embodiment and a comparative example of the air supply system;

FIG. 5 illustrates a block diagram of the schematic structure of an air supply system;

FIG. 6 shows a relation between the volume of air discharged from the rectification apparatus and the pressure drop by the rectification apparatus;

FIG. 7 illustrates the second illustrative embodiment and a comparative example of the air supply system; and

FIG. 8 illustrates the third illustrative embodiment and a comparative example of the air supply system.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiments of the present invention are described with reference to the drawings. It is noted that, in the following description of the embodiments, the same components are denoted with the same reference numerals and the explanation thereof will be omitted or simplified.

First Embodiment

FIG. 1 illustrates a block diagram of a fuel cell system 1 using an air supply system 21.

The fuel cell system 1 has a fuel cell 10, a supply apparatus 20 which supplies hydrogen gas and air to the fuel cell 10, and a control apparatus 30 which controls the fuel cell 10 and the supply apparatus 20.

In the fuel cell 10 as described above, when the anode (positive electrode) is supplied with hydrogen gas and the cathode (negative electrode) is supplied with air containing oxygen, power is generated by way of the electrochemical reaction.

The supply apparatus 20 is configured to include an air supply system 21 which supplies air to the cathode of the fuel cell 10, and a hydrogen tank 22 and an ejector 28 which supply hydrogen gas to the anode.

The air supply system 21 is connected to the cathode of the fuel cell 10 via an air supply path 23.

The cathode of the fuel cell 10 is connected with an air exhaust path 24. The end of this air exhaust path 24 has a back-pressure valve 241.

The hydrogen tank 22 is connected to the anode of the fuel cell 10 via a hydrogen supply path 25. This hydrogen supply path 25 includes the above-described ejector 28. In the hydrogen supply path 25, a pressure adjustment valve 251 is disposed between the hydrogen tank 22 and the ejector 28.

The anode of the fuel cell 10 is connected with a hydrogen exhaust path 26. The end of this hydrogen exhaust path 26 has a purge valve 261. At a position in the hydrogen exhaust path 26 in a range from the purge valve 261 to the anode, the hydrogen exhaust path 26 branches and is connected to the above-described ejector 28.

Through the branch path of the hydrogen exhaust path 26, the ejector 28 recovers hydrogen gas which has flowed into the hydrogen exhaust path 26 to reflux the hydrogen gas in the hydrogen supply path 25.

The above-described air supply system 21, back-pressure valve 241, purge valve 261, and pressure adjustment valve 251 are controlled by a control apparatus 30.

Power generation by the fuel cell 10 is performed by a procedure described below.

More specifically, the purge valve 261 is closed and the pressure adjustment valve 251 is opened, and hydrogen gas is supplied from the hydrogen tank 22 via the hydrogen supply path 25 to the anode of the fuel cell 10. The air supply system 21 is driven to supply air via the air supply path 23 to the cathode of the fuel cell 10.

The hydrogen gas and air supplied to the fuel cell 10 are used for power generation. Thereafter, the hydrogen gas and air as well as residual water (e.g., generated water at anode side) flow from the fuel cell 10 into the hydrogen exhaust path 26 and the air exhaust path 24. Meanwhile, since the purge valve 261 being closed the hydrogen gas flowing to the hydrogen exhaust path 26 is refluxed to the ejector 28 and reused.

Then, the purge valve 261 and the back pressure valve 241 are opened to an appropriate extent to exhaust hydrogen gas, air, and residual water from the hydrogen exhaust path 26 and the air exhaust path 24.

FIG. 2 illustrates a block diagram of the schematic structure of the air supply system 21.

The air supply system 21 includes a compressor 41 which draws in air as gas to discharge the drawn in air at an increased pressure, and a silencer 42 which reduces the noise produced in the compressor 41.

An inlet of the compressor 41 is connected with an intake flow path 43 in which air drawn in by the compressor 41 flows.

The inlet side of the intake flow path 43 has an air intake 431 in which a filter (not shown) filters out dust in air.

The compressor 41 is connected to the silencer 42 via a discharge flow path 44 in which air discharged from the compressor 41 flows.

When the compressor 41 is driven in this air supply system, outside air is introduced via the air intake 431 to the intake flow path 43. The compressor 41 draws in this air via the intake flow path 43 to discharge the drawn in air with at an increased pressure. The discharged air is introduced to the silencer 42 via the discharge flow path 44. The noise of the air is reduced by the silencer 42. Then, the air is supplied to the cathode electrode of the fuel cell 10.

In the discharge flow path 44 and the intake flow path 43, a rectification apparatus 45A as the first rectification apparatus and a rectification apparatus 45B as the second rectification apparatus for rectifying gases are disposed in the vicinity of the compressor 41.

FIG. 3 illustrates a partial enlarged view of the intake flow path 43 and the discharge flow path 44.

The rectification apparatuses 45A and 45B have a honeycomb structure in which a plurality of plate-like members 452 divide, in a lattice-like manner, the internal spaces of the discharge flow path 44 and the intake flow path 43 to provide a plurality of rectification channels 451 extending along the discharge flow path 44 and the intake flow path 43.

The rectification apparatus 45A immediately rectifies the flow of air discharged from the discharge outlet of the compressor 41 to equalize the pressures variations, thereby reducing the pulsation noise and vibration due to the driving of the compressor 41.

The rectification apparatus 45B rectifies the flow of air to be drawn in by the inlet of the compressor 41, thereby reducing noise such as wind roar noise (also referred to as siren noise) of the air.

Illustrative Embodiment 1

FIG. 4 shows the first illustrative embodiment and a comparative example of the air supply system. More specifically, FIG. 4 shows a relation between noise level and a compressor revolution speed when the discharge outlet of a compressor includes the rectification apparatus.

As can be seen from FIG. 4, an air supply system including the rectification apparatus can reduce noise in a wide range of revolution speeds more than in a case of the air supply system not including the rectification apparatus.

Especially, noise is greatly reduced at medium and high revolution speeds.

This embodiment provides the following advantages.

1. The rectification apparatus 45 for rectifying air is disposed at the intake flow path 43 and the discharge flow path 44. Therefore, the turbulence associated with a shock wave caused by air intake and discharge is rectified and the sudden change of the air flow is suppressed so as to reduce the noise level in a wide range of revolution speeds. As a result, noise caused by air intake or discharge of air can be reduced in a wide frequency band. With only the addition of the rectification apparatuses 45 disposed at the inlet and discharge outlet of the compressor 41, along with the space and cost can be reduced.

2. The rectification apparatus 45 constituted of a plurality of rectification channels 451 allows, even when drawn in air or discharged air flows backward, the air to stay in the rectification path 451, thereby preventing the backflow of the air.

Second Embodiment

The second embodiment differs from the first embodiment in the position and shape of the rectification apparatuses 45A and 45B.

More specifically, as shown in FIG. 5, a rectification apparatus 45A in an air supply system 21A is abutted with the discharge outlet of the compressor 41 and a rectification apparatus 45B is abutted with the inlet of the compressor 41.

It is assumed that the number of rectification channels 451 of the rectification apparatuses 45A and 45B to the cross-sectional area of the discharge flow path 44 and the intake flow path 43 represent a density of the rectification apparatus. It is also assumed that the lengths of the rectification apparatuses 45A and 45B in the direction along which the discharge flow path 44 and the intake flow path 43 extend represent a length of the rectification apparatus.

FIG. 6 shows a relation between the volume of air discharged from the compressor and the pressure drop by the rectification apparatus. In FIG. 6, a curve showing the change in the pressure drop of the rectification apparatus was obtained by approximating experiment values using a polynomial equation.

When the density or length of the rectification apparatus is increased, the noise reduction effect in the discharge and intake is increased, but the pressure drop by the rectification apparatus also increases as shown in FIG. 6. Therefore, the density and length of the rectification apparatuses 45A and 45B are determined so as not to result in the pressure drop exceed the maximum value of the acceptable values.

Illustrative Embodiment 2

FIG. 7 illustrates the second illustrative embodiment and a comparative example of the air supply system. More specifically, FIG. 7 shows a relation between a noise level and a compressor revolution speed when the rectification apparatus provided at the discharge outlet of the compressor has a different length.

As can be seen from FIG. 7, when the air supply system has a rectification apparatus having a length 2L, the noise is reduced in a wider range of revolution speeds than in a case of the rectification apparatus having a length L.

Illustrative Embodiment 3

FIG. 8 illustrates the third illustrative embodiment and a comparative example of the air supply system. More specifically, FIG. 8 shows a relation between a noise level and a compressor revolution speed when the density of the rectification apparatus provided at the discharge outlet of the compressor is changed.

As can be seen from FIG. 8, when the air supply system has a rectification apparatus having a density 2D, the noise is reduced in a wider range of revolution speed than in a case of the rectification apparatus having a density D.

This embodiment provides the following advantages in addition to the above-described advantages 1 and 2.

3. The rectification apparatuses 45A and 45B abutted with the discharge outlet and inlet of the compressor 41 can significantly reduce noise caused when gas is discharged and drawn in.

4. The rectification apparatuses 45A and 45B have a maximum length in the direction along which the discharge flow path 44 and the intake flow path 43 extend within an acceptable range of the pressure drop by the rectification apparatuses 45A and 45B. Thus, the noise caused by gas discharge and intake can be reduced while ensuring the discharge pressure required for the air supply system 21.

5. The rectification apparatuses 45A and 45B has a honeycomb structure constituted of a plurality of rectification channels 451 extending along the discharge flow path so that the number of rectification channels 451 for the cross-sectional area of the discharge flow path 44 or the intake flow path 43 can be maximized resulting in the pressure drop by the rectification apparatuses 45A and 45B within the acceptable range. Thus, the noise during gas discharge can be significantly reduced while ensuring the discharge pressure required for the air supply system 21.

It is noted that the present invention is not limited to the above embodiments and that changes or modifications to the present invention within a range within which the objective of the invention can be achieved are included in the present invention. 

1. An air supply system, comprising: a compressor which draws in gas to discharge the gas drawn in, at an increased pressure; an intake flow path through which the gas drawn in by the compressor flows; a discharge flow path through which the gas discharged from the compressor flows; and a first rectification apparatus disposed in the vicinity of the compressor in the discharge flow path and rectifies the gas flowing therein.
 2. The air supply system according to claim 1, further comprising: a second rectification apparatus disposed in the vicinity of the compressor in the intake flow path and rectifies the gas flowing therein.
 3. The air supply system according to claim 1, wherein the first rectification apparatus is abutted with a discharge outlet of the compressor.
 4. The air supply system according to claim 1, wherein the first rectification apparatus has a maximum length in a direction along which the discharge flow path extends resulting in a pressure drop by the first rectification apparatus within an acceptable range.
 5. The air supply system according to claim 1, wherein the first rectification apparatus has a honeycomb structure comprised of a plurality of rectification channels extending along the discharge flow path, and a number of the rectification channels to a cross-sectional area of the discharge flow path is maximum resulting in the pressure drop by the first rectification apparatus within the acceptable range.
 6. An air supply system, comprising: a compressor which draws in gas to discharge the gas drawn in, at an increased pressure; an intake flow path through which the gas drawn in by the compressor flows; a discharge flow path through which the gas discharged from the compressor flows; and a rectification apparatus disposed in the vicinity of the compressor in the intake flow path and rectifies the gas flowing therein. 